Excerpts from NASA Procedural Requirements, NPR 8715.3B (effective April 04, 2007):
c. Not use hand-held communication devices while the vehicle is motion except for emergency, security, and fire vehicles during official operations.
Note: This includes cell phones, walkie-talkies (FRS, Part 90, ham), Ames EDACS M/A-Coms, M-RKs, and other hand-held wireless communication devices.
For complete regulation, see http://nodis3.gsfc.nasa.gov/displayDir.cfm?Internal_ID=N_PR_8715_003B_&page_name=Chapter3
Note: Above regulation is applicable to federal property, NASA Ames Research Center, not outside the Ames boundary.
New California Vehicle Code cellphone law
From http://www.dmv.ca.gov/cellularphonelaws/dl208_03cell_phone.pdf
However, while on Ames property you cannot use walkie-talkies while driving.